1. Field of the Invention
The invention relates generally to storage controllers of storage systems and more specifically relates to apparatus and methods for improved efficiency in processing of virtual to physical mapping meta-data in a storage controller.
2. Related Patents
This patent is related to commonly owned U.S. patent application Ser. No. 12/854,765 entitled APPARATUS AND METHODS FOR MANAGING EXPANDED CAPACITY OF VIRTUAL VOLUMES IN A STORAGE SYSTEM and is related to commonly owned U.S. patent application Ser. No. 12/854,720 entitled APPARATUS AND METHODS FOR REAL-TIME ROUTING OF RECEIVED COMMANDS IN A SPLIT-PATH ARCHITECTURE STORAGE, both of which are hereby incorporated by reference.
3. Discussion of Related Art
Virtualized storage systems define one or more virtual volumes for use by attached host systems. Each virtual volume comprises a range of contiguous logical addresses (e.g., logical block addresses or LBAs) that are mapped to some physical storage locations on storage devices associated with the storage system. A storage controller of the storage system is coupled with the attached host systems and with physical storage devices associated with the storage system. The storage controller receives I/O requests from attached host systems and/or from storage related services provided within the storage system. The storage controller then translates or maps the logical addresses affected by the I/O request into corresponding physical storage locations.
The mapping meta-data structure for a simple logical/virtual volume is typically a relatively simple table structure that maps logical addresses to corresponding physical storage locations. Such a relatively simple meta-data structure may typically be stored in a cache memory or other high speed memory for rapid access to thus reduce overhead processing of the storage controller. Use of such mapping meta-data structures is often referred to as “walking” the mapping meta-data structure. A “walk” of the mapping structure for a simple read or write access to a simple virtual volume is relatively rapid and uses relatively little CPU and memory bandwidth of the storage controller—thus, imposing a relatively small overhead processing burden on the storage controller as it may impact overall storage system performance.
In some storage systems, the storage controller of the storage system (or other Components—e.g., network appliances associated with the storage system) may provide various enhanced data services within the storage system. These enhanced data services provide a number of data services beyond simple read and write access to data stored on a simply logical/virtual volume. For example, some virtualized storage systems provide data services within the storage system for automated synchronous mirroring (e.g., mirroring of data to another volume such as for reliability or for remote replication of data). Still other exemplary enhanced data services may provide for automated snapshot generation (i.e., to create shadow or snapshot copies of the contents of a virtual volume such as for replication or backup data services).
These and other exemplary enhanced data services may involve far more complexity in their respective access to mapping meta-data and other meta-data pertaining to accessing the virtual volume for the enhanced services. For example, access to a synchronous mirrored volume of a virtual volume may, at a minimum, involve accessing mapping meta-data for two virtual/logical volumes. Or, for example, access to automatically generated snapshots may entail accessing significantly more meta-data to identify a particular point in time snapshot of the contents of a logical/virtual volume.
This added complexity in providing virtual to physical mapping where a volume is utilizing enhanced data services can add significant overhead to the processing of the storage controller in “walking” the mapping and other meta-data structures associated with the virtual volumes. This added overhead processing can rise to a level that notably, negatively impacts overall performance of the storage system.
Thus, it is an ongoing challenge to reduce the overheard processing involved in managing meta-data for virtual volumes managed by a storage controller of a virtualized storage system.